my tamagotchi has a black screen with a Z on it how do i wake it up?

It wakes up when it is ready to wake up. This is usally around the time most people wake up. Even though there is no deffinate time, it shouldn't be asleep for longer than 15 hours at one time. If you set the time to about 12pm, all species of tamagotchi should be awake by then. Make sure you correct the time later though, or it will be awake at night and may die.